Flow/flame and emissions fields of premixed oxy-methane stratified flames in a dual annular counter-rotating swirl burner

Abstract

Dual Annular Counter-Rotating Swirl (DACRS) premixed oxy-methane flames for nine different cases were studied numerically in a Dual-Stage Lean Premixed (DLPM) combustor for gas turbine combustion applications. The combustor consists of two streams, a primary central stream and a secondary annular one swirling in opposing directions. For all cases, the primary and secondary oxygen fraction (OF: O2%vol. in O2/CO2 oxidizer) was maintained at 30%, and the equivalence ratios (φ) of the primary and secondary streams were set to 0.9 and 0.55, respectively. Three different velocities were investigated for the primary central stream, and for each primary stream velocity, three different secondary velocities were considered to explore flow/flame interactions. The results show that: for all primary flow velocities, decreasing the secondary flow velocity led to the flame becoming thin and slightly elongated. The zone of peak local temperatures was concentrated in the flame core downstream of the center-body near the primary flow inlet as the secondary flow velocity was reduced. The magnitude of axial velocity has an effect on the flow distribution up to the first one-third section of the combustor. The mixture velocity varies inversely with Da number towards the combustor's exit. The thermal effect of secondary stream velocity starts around 40% away from the burner surface. Species distributions show that complete combustion is achieved and excess oxygen leaves the combustor with products due to the lean mixture of the secondary flow stream. The peak of product formation rate (PFR) is affected by flow streams velocities. Stable flames with reduced emissions were obtained over wide range of inlet velocities indicating the effectiveness of DLPM combustion approach for wider operability of gas turbine combustors.